Does MAXU return 0 or 1?
No. It returns the original XLEN-bit value selected from rs1 or rs2 by the comparison rule.
MAXU
RISC-V MAXU Instruction Details
Instruction ManualR-typeReturn the maximum of rs1 and rs2 using unsigned comparison.
Instruction Syntax
maxu rd, rs1, rs2
Operand Breakdown
rd: x0–x31; receives the selected operand's original XLEN-bit pattern; writes to x0 are discarded.
rs1, rs2: compared as unsigned integers to select the larger value; source/destination overlap reads the values before writeback.
RV32/RV64, requiring Zbb 1.0; 32-bit R-type encoding with no immediate operand.
BZbbBit ManipulationInteger Operation
Instruction Behavior
MAXU is a Zbb integer min/max instruction. It compares x[rs1] and x[rs2] as unsigned values and writes the original XLEN-bit value that is larger under that ordering to rd.
MAXU Decode And Execute Animation
Starts with machine-code field decoding, then shows operand reads, instruction-specific execution, and ISA-visible state update.
rd
rs1
rs2
maxu
,
,
Execution Context
Assumes RV32/RV64 with Zbb enabled, fixed initial register values, and PC=0x2000; instruction fetch succeeds and there are no asynchronous interrupts. These educational steps do not represent processor cycles.
t1(x6)
0x00000014
a0(x10)
0x00001000
31..25
24..20
19..15
14..12
11..7
6..0
0000101
funct7
01010
rs2
00110
rs1
111
funct3
00101
rd
0110011
opcode
Execution Data Path
instruction
0x0AA372B3
opcode
0110011 -> OP
funct3
111 -> MAXU
funct7
0000101 -> Zbb MIN/MAX selector
rd / rs1 / rs2
t0(x5) / t1(x6) / a0(x10)
integer comparison and selection
Not computed
x5
t0(x5) = 0x00003001; pc = 0x00002000
Current Step
Concept Step: receive the 32-bit instruction encoding
The machine code is split by the current instruction format; the animation starts from encoding/decode.
encoding: 0x0AA372B3
syntax : maxu t0(x5), t1(x6), a0(x10)
Pending result: Not computed
Current architectural state
t0(x5) = 0x00003001; pc = 0x00002000
This animation shows ISA-visible decode and state changes, not any specific CPU pipeline, cache, prediction, or timing implementation.
Quick Understanding & Search Notes
MAXU selects between rs1 and rs2 using unsigned ordering and returns the selected original XLEN-bit pattern, not a comparison bit.
Forms with U use unsigned ordering; forms without U use two's-complement signed ordering.
MAXU operands and result are XLEN-wide integer-register values.
Common Usage Scenarios
Integer Comparison
Understand this scenario with real code like «maxu x10, x11, x12 ; x10 = unsigned_max(x11, x12)».
Integer Min/Max
Understand this scenario with real code like «maxu x10, x11, x12 ; x10 = unsigned_max(x11, x12)».
Pre-Use Checklist
Syntax Check
- RV32/RV64 requires enabled Zbb 1.0; register operands select x0–x31.
- Syntax has only rd, rs1 and rs2, with no rs3 or immediate operand.
Semantic Check
- MAXU selects between rs1 and rs2 using unsigned ordering and returns the selected original XLEN-bit pattern, not a comparison bit.
- Overlapping operands read values before writeback; x0 is always zero and writes to x0 are discarded.
Pitfalls / Common Confusions
MAXU uses unsigned comparison; use MAX for signed comparisons.
The result is the selected original register value, not Boolean 0/1.
MAXU and MAX differ only in comparison signedness; the selected original bit pattern is written.
FAQ
How do I choose between MAXU and MAX?
Use the U form when data is ordered as unsigned; use the non-U form for signed two's-complement ordering.